Java Holiday Calendar 2016 (Day 10): MapStream

Today's tip is about the open-source class MapStream, which allows us to stream not only over elements, but over a pair of key value elements and make changes either to the keys, values, or both.

You can find the source code for MapStream here together with some examples of how to use it. It is free, so go ahead and use or copy it in your application! MapStream is a part of Speedment.

With MapStream, you can do this:

Map<String, Integer> numberOfCats = new HashMap<>();

numberOfCats.put("Anne", 3);
numberOfCats.put("Berty", 1);
numberOfCats.put("Cecilia", 1);
numberOfCats.put("Denny", 0);
numberOfCats.put("Erica", 0);
numberOfCats.put("Fiona", 2);

System.out.println(
  MapStream.of(numberOfCats)
      .filterValue(v -> v > 0)
      .sortedByValue(Integer::compareTo)
      .mapKey(k -> k + " has ")
      .mapValue(v -> v + (v == 1 ? " cat." : " cats."))
      .map((k, v) -> k + v)
      .collect(Collectors.joining("\n"))
);

This would produce the following:

Cecilia has 1 cat.
Berty has 1 cat.
Fiona has 2 cats.
Anne has 3 cats.

Read more about MapStream here.

Follow the Java Holiday Calendar 2016 with small tips and tricks all the way through the winter holiday season.